1. Field of the Invention
The present invention relates to a magnetic recording medium which has a recording layer formed in a concavo-convex pattern.
2. Description of the Related Art
There has been a remarkable increase in areal density of magnetic recording media such as hard disks by various improvements including reduction in the grain size of magnetic particles forming the recording layer, material changes, and increased precision in the processing of magnetic heads, and a further improvement in the areal density is expected.
However, problems such as a limitation in the processing of magnetic heads, side fringes due to the spread of a magnetic field, and crosstalk have become pronounced, so that increase in the areal density by a conventional improvement method has reached its limitation. Thus, magnetic recording media such as discrete track media and patterned media have been proposed as a candidate for a magnetic recording medium which can realize further increase in the areal density (refer to, for example, Japanese Patent Laid-Open Publication No. Hei 9-97419). In such a magnetic recording medium, a recording layer is formed into a predetermined concavo-convex pattern.
Namely, since information is recorded on convex portions of the concavo-convex pattern, it is possible to restrain a side fringe, crosstalk, and the like between a convex portion and an adjacent convex portion. Forming the recording layer in a concavo-convex pattern also has the effect of preventing a magnetic head from being adsorbed onto the surface of the magnetic recording medium.
When concavities and convexities exist at the surface of the magnetic recoding medium, on the other hand, there are cases where stable flying characteristics of the head cannot be obtained.
To solve such a problem, it is conceivable that a non-magnetic material is deposited over the recording layer in a concavo-convex pattern for the purpose of filling concave portions with the non-magnetic material, followed by removing a surplus of the non-magnetic material above the recording layer to flatten the surface thereof.
A deposit technology such as sputtering, which is used in the field of semiconductor manufacturing, is available as a method for depositing a non-magnetic material. Also, a processing technology such as CMP (chemical mechanical polishing), which is used in the field of semiconductor manufacturing, is available as a method for removing a surplus non-magnetic material above the recording layer to flatten the surface.
The non-magnetic material, however, is deposited into a concavo-convex shape in accordance with the concave-convex shape of the recording layer. The deposited non-magnetic material is removed all over the surface during a flattening process, while concavities and convexities at the surface are gradually flattened. Thus, it is difficult to completely flatten the concavities and convexities, even if the non-magnetic material is removed up to the top face of the recording layer.
In the CMP method, it is difficult to precisely control the amount of processing (thickness) in the order of nanometers. Accordingly, there are cases where after the non-magnetic material above the recording layer is removed, a part of the recording layer is removed together with the non-magnetic material, and hence difference in the height of the surface contrarily increases because of difference between the processing rates of both.
In other words, it is difficult to completely flatten the surface, even if the non-magnetic material is deposited over the recording layer in the concavo-convex pattern to fill the concave portions with the non-magnetic material, and the surplus non-magnetic material above the recording layer is removed. A concavo-convex shape, to which the concavo-convex pattern of the recording layer is reflected, remains in the surface, and there are cases where stable flying characteristics of the head cannot be obtained due to such a concavo-convex shape.